Low density lipoprotein ("LDL") and high density lipoprotein ("HDL") are very important components of blood. LDL is involved in transporting cholesterol to the peripheral organs and cells. HDL is involved in transporting cholesterol away from the peripheral organs and cells to the liver. High blood plasma LDL cholesterol levels are correlated with the development of coronary heart disease and heart attacks. On the other hand, high HDL levels appear to reduce the adverse affect of high LDL levels. The ratio of LDL to HDL is therefore now an important predictor for the susceptibility or resistance to coronary heart disease and heart attacks, and as a factor in developing diets.
Precise measurements of HDL lipoprotein levels are therefore highly desirable for clinical purposes. HDL cholesterol is currently usually determined by first measuring total blood plasma cholesterol, then LDL is precipitated out, and then the level of total cholesterol left in the supernatant is measured. The difference is assumed to be HDL. While deducing HDL in this way gives a rough estimate, it assumes that there is no other type of cholesterol present in the sample, and the method is limited by the ability of the LDL precipitant to selectively and effectively pull the LDL out of solution. There are currently no better practical methods to assay levels of HDL cholesterol (albeit there is also an ultracentrafuge method which is very costly and time consuming). The development of a more practical method for directly measuring HDL cholesterol is therefore highly desirable.
In separate unrelated work a red blood cell haemagglutinating factor has been isolated in boar seminal plasma. See J. Boursnell et al., 11 J. Reprod. Fert. 139-144 (1966). It is present in boar vesicular secretion, but not in epididymal seminal plasma or in boar spermatozoa. See also J. Boursnell et al., 19 J. Reprod. Fert. 157-266 (1969) (protein H in factor agglutinates sperm cells); H. Moore et al., 47 J. Reprod. Fert. 39-45 (1976) (factor secreted by seminal vesicle accessory gland); D. Schellpfeffer et al., 23 J. Reprod. Fert. 291-98 (1970) (two sizes of proteins active in factor); T. Roberts et al., 41 J. Reprod. Fert. 489-92 (1974) (lipid site on red blood cell may cause agglutination). The disclosure of these articles and of all other articles recited herein are incorporated by reference as if fully set forth herein. While there has been some interest in studying this factor and whether it contains any lipoprotein, to date there has been no suggestion in the art that this factor has any utility vis a vis testing for HDL levels.